The present invention relates to peptides and their derivatives which are useful for the diagnosis and monitoring of synucleinopathies. These are diseases associated with abnormalities in one or more of the synucleins and include some important neurodegenerative conditions, for example Parkinson's disease (PD), dementia with Lewy bodies (DLB), Alzheimer's disease (AD) and multiple system atrophy (MSA). The synucleins are also expressed at abnormally high levels in various tumours (e.g. breast, ovarian) in human cancer.
The synucleins are a family of small proteins (˜14 kDa) that are expressed at high levels in nervous tissue. The three members of the family (α-, β-, and γ-synuclein) are the products of three genes present on different chromosomes. Convergent genetic and biochemical evidence suggests that the deposition of insoluble α-synuclein aggregates or fibrils is an important step in the development of several synucleinopathies.
The first indication of an involvement of α-synuclein in the pathogenesis of disease came from the isolation of one of its proteolytic fragments from purified amyloid of Alzheimer's diseased (AD) brains. This α-synuclein fragment, representing about 10% of the sodium dodecyl sulphate (SDS) insoluble material, was named non-Aβ-component of AD amyloid (NAC). Amino acid sequencing revealed that NAC comprised at least 35 amino acids, although the N-terminal residues could not be assigned with certainty because of the specificity of the enzyme used in sequencing. These 35 amino acids were later shown to correspond to residues 61-95 of a 140 amino-acid precursor (NACP). NACP was found to be identical with the protein called α-synuclein.
A clear genetic link with PD was established when it was shown that three different mutations in the α-synuclein gene were found in rare inherited forms of this disease. One mutation, α-synuclein (A53T), has been found in certain Italian and Greek families, and results in an Ala53 to Thr substitution. The other mutation, α-synuclein (A30P), has been found in a family of German origin, and results in an A1a30 to Pro change, and the last mutation E46K was found in familial Parkinsonism and DLB. Furthermore, Genetic duplications and triplications of the SNCA locus have also been reported in familial cases of PD suggesting that increase in gene dosage of SNCA, which concurrently results in an increase in levels of wild-type α-synuclein protein, is also pathogenic. Duplications of SNCA closely resemble idiopathic PD with late-age onset, slow progression and the absence of dementia and cognitive decline. Alternatively, SNCA triplications, result in early-onset PD with faster progression and dementia.
Additionally, lesions in the brain known as ‘Lewy bodies’ and ‘Lewy neurites’ constitute the main pathological features in the brains of patients with PD and DLB. These Lewy bodies and Lewy neurites contain α-synuclein aggregates. Additional immunohistochemical and immunoelectron microscopy studies have shown that α-synuclein is also associated with pathological lesions in other neurodegenerative diseases, sometimes involving non-neuronal cells, such as the glial cytoplasmic inclusions found in MSA. Thus PD, AD, DLB and MSA are herein referred to collectively as synucleinopathies.
It has recently been reported that lesions similar to those found in the human synucleinopathic diseases can be created in transgenic animals. The transgenic animals express high levels of human wild-type or mutant α-synuclein protein and progressively develop many of the pathological conditions associated with synucleinopathic diseases. These findings implicate α-synuclein protein aggregate deposition in the pathophysiology of the synucleinopathic diseases. Interestingly, the three human α-synuclein mutations appear to accelerate the aggregation process. The full amino acid sequence of human wild-type α-synuclein is provided as SEQ. ID No. 1.